Aerobic Respiration: Pyruvate into the Mitochondria
Glycolysis ends in the cytosol with pyruvate, and at that junction the cell must decide how far to push the oxidation of glucose. Fermentation offers only a partial answer: it releases less than seven per cent of the energy in glucose and leaves behind acid or alcohol. Aerobic respiration is the genuine harvest.
This quiz follows pyruvate across the mitochondrial threshold and tests the gateway reaction of aerobic respiration:
- Why complete oxidation of organic substances requires oxygen
- Why the mitochondria are the site of these steps in eukaryotes
- How pyruvate is transported from the cytoplasm into the mitochondrial matrix
- The two crucial events that define aerobic respiration and where each occurs
- The oxidative decarboxylation of pyruvate to acetyl CoA by pyruvic dehydrogenase
Expect questions on coenzymes, the products of the pyruvate dehydrogenase reaction, and the fate of acetyl CoA as it enters the tricarboxylic acid cycle.
Q1. Aerobic respiration is best defined as the process that leads to:
Aerobic respiration leads to complete oxidation of organic substances in the presence of oxygen, releasing ##\ce{CO2}##, water and a large amount of energy from the substrate.
Q2. In eukaryotic cells, the steps of aerobic respiration take place within the:
In eukaryotes these steps take place within the mitochondria, and the process requires a supply of ##\ce{O2}##.
Q3. For aerobic respiration to occur inside the mitochondria, the final product of glycolysis must first be:
Pyruvate, the final product of glycolysis formed in the cytosol, is transported from the cytoplasm into the mitochondria before aerobic respiration can proceed.
Q4. Which of the following is one of the two crucial events of aerobic respiration?
The first crucial event is the complete oxidation of pyruvate by stepwise removal of all the hydrogen atoms, leaving three molecules of ##\ce{CO2}##.
Q5. The second crucial event of aerobic respiration involves the passing on of electrons removed as part of hydrogen atoms to:
The second crucial event is the passing on of the electrons removed as part of the hydrogen atoms to molecular ##\ce{O2}##, with simultaneous synthesis of ATP.
Q6. The complete oxidation of pyruvate, leaving three molecules of ##\ce{CO2}##, takes place in the:
The first process, complete oxidation of pyruvate, takes place in the matrix of the mitochondria, while the second process is located on the inner membrane.
Q7. The passing on of electrons to molecular oxygen with simultaneous ATP synthesis is located on the:
The second crucial event, electron transfer to ##\ce{O2}## with ATP synthesis, is located on the inner membrane of the mitochondria.
Q8. After entering the mitochondrial matrix, pyruvate undergoes oxidative decarboxylation catalysed by:
Pyruvate undergoes oxidative decarboxylation by a complex set of reactions catalysed by pyruvic dehydrogenase.
Q9. Which coenzymes are required for the reactions catalysed by pyruvic dehydrogenase?
The reactions catalysed by pyruvic dehydrogenase require the participation of several coenzymes, including ##\ce{NAD+}## and coenzyme A.
Q10. The products of the oxidative decarboxylation of pyruvic acid by pyruvic dehydrogenase are:
The reaction converts pyruvic acid with CoA and ##\ce{NAD+}## into acetyl CoA, ##\ce{CO2}##, ##\ce{NADH}## and ##\ce{H+}##.
Q11. How many molecules of ##\ce{NADH}## are produced from the metabolism of the two molecules of pyruvic acid formed from one glucose molecule during glycolysis?
During this process, two molecules of ##\ce{NADH}## are produced from the metabolism of two molecules of pyruvic acid derived from one glucose molecule.
Q12. The acetyl CoA formed from pyruvate then enters a cyclic pathway known as the:
The acetyl CoA then enters a cyclic pathway, the tricarboxylic acid cycle, more commonly called Krebs' cycle.
Q13. In both lactic acid and alcohol fermentation, the energy released from glucose is:
In both fermentations less than seven per cent of the energy in glucose is released, and not all of it is trapped as high-energy bonds of ATP.
Q14. Which statement correctly contrasts fermentation with aerobic respiration?
Fermentation is hazardous since either acid or alcohol is produced, while aerobic respiration completely oxidises the substrate and releases ##\ce{CO2}##, water and a large amount of energy.
Q15. The three major ways in which different cells handle the pyruvic acid produced by glycolysis are:
There are three major ways in which different cells handle pyruvic acid produced by glycolysis: lactic acid fermentation, alcoholic fermentation and aerobic respiration.